<VV> Anyone using MegaSquirt on a Corvair? (long)

[FrankCB at aol.com]

Chuck,
    From your description it appears that you are using  the stock 180 
distributor with the stock pressure retard.  If that's true  then you could achieve 
another 20% improvement in gas mileage by adding in a  vacuum advance instead 
of the stock pressure retard on the side of the  distributor.  With the stock 
pressure retard, the ignition timing stays  CONSTANT from idle to about 4000 
rpm or until you develop some boost  pressure.  So for highway driving under 
vacuum conditions, you're losing a  lot of economy.  You already have the 
SafeGuard to provide timing retard as  needed to prevent pinging/knocking.  See the 
description in the Turbo  Chapter of the Corvair Basics manual.
    Thanks for the good details on your  installation.
    Regards,
    Frank "timing is everything" Burkhard
 
In a message dated 10/30/2007 3:12:06 PM Eastern Daylight Time,  
chuckriblett at msn.com writes:

I have  been driving a turbocharged Corvair with fuel injection controlled by
a  MegaSquirt controller for about a year.  This is basically a 95 HP  engine
with forged pistons, Otto cam, 180HP turbocharger and 180HP  distributor with
SafeGuard ignition.  I machined a throttle body that  fits between the
turbocharger and the original air filter housing.   The throttle plate
diameter is 1.8 inches compared to the YH carburetor  throttle plate of 1.5
inches resulting in much greater airflow than the  carburetor.

I have never driven for best fuel economy, but I have kept  records.  With
fuel injection and a wide band oxygen sensor the car  has been getting 20-22
MPG despite using the increased performance.   For comparison, with the YH
carburetor and original metering rod and jet, I  got 13-16 MPG.  After much
testing using a narrow band oxygen sensor  and machining custom metering
rods, I was able to get 17-19.5 MPG using the  carburetor.

Setting up the fuel tables is fairly easy if you use a wide  band oxygen
sensor for feedback.  The baseline tables are created  based on the engine
size and the number and flow rate of the fuel  injectors.  With the
MegaSquirt I controller, you drive around  collecting data on a laptop
computer with MegaTune software.  Then you  use MegaLogViewer to modify the
fuel tables.  With MegaSquirt II,  AutoTune is available to adjust the fuel
tables as you drive.  I  believe that you can easily pay for the $200 wide
band oxygen sensor system  with the improved fuel economy.

The engine started the first time as  soon as the fuel lines were
pressurized.  After setting the idle  speed, I was able to drive the car
gently and collect data.  After a  few drives around the neighborhood
collecting data and then modifying the  fuel table, I was able to drive the
car normally.  I continued to make  small adjustments whenever I noticed an
area that could be  improved.

The engine now starts immediately every time without any of  the flooding and
vapor lock problems of the carburetor.  The increase  in torque available for
passing at highways speeds is truly  impressive.

The hardest part of the installation was routing a fuel  return line and
connecting it to the gas tank.  The most time  consuming task was fabricating
a wiring harness.  I mounted the  electronics on the shelf above the
transaxle (early coupe) away from the  engine compartment heat.

The original version of the throttle body had  the injectors before the
throttle plate.  This resulted in fuel  dripping out at the air filter flange
particularly in cold weather.   For the current version, the injectors are
mounted after the throttle  plate.  Since the injectors are mounted on the
vacuum side of the  throttle plate, there have been no fuel leakage problems.

I don't think  that a low-pressure throttle body with the injector(s) above
the throttle  plate can be mounted sideways without fuel leakage problems.

Future  plans call for using a MegaSquirt II controller for ignition control.
I am  also working on throttle bodies for a 140HP engine in another  car.

Chuck







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